Good Uses For Modem Teaming?

legana asks: "We are just about to install multiple cable modems at our office and we were wondering how to make the best use of them. What software/hardware is available that will allow us to share the modems across the network but still allow certain users priority (for uses such as video-conferencing, etc.)? Is it better to share all the modems across the entire network or break the network into subnets each with their own group of modems? Does connecting multiple modems to one computer really increase the bandwidth available?"

Replicate Nameservers?

[dragonfly_blue]

I'm not sure if this would work, or not, but if you've got the budget for multiple broadband channels, maybe you have the budget for this, too. This would be especially effective if you do hosting for multiple domains, but any company could implement it.

Set up two DNS nameservers, running perhaps a *BSD or Linux, one on the gateway of each modem. Then set them up as the primary and secondary DNS servers for the client machines on the network.

You'd have to tune them to network requests at this point, but hopefully it would allow you to resolve DNS through whichever modem was fastest/least busy at the time, and this could help distribute the traffic more evenly.

You could also set up proxy services in this manner, and allocate bandwidth and services as you see fit. (e.g. assign FTP to run through a proxy on one of the lines, HTTP to run on the other, etc.) If your videoconferencing software supports it, you might even be able to run it through the proxy, and keep a line (mostly) dedicated to that.

I suppose you could script something to allow changeovers to another line, should one be bogged down with a session, but I don't know how I'd implement something like that... it's too early and I just got coffee.

Good luck, maybe post your results of this, (even if you go a different route I'd like to hear about it!) on one o' them new-fangled "web sites" you kids are talking about these days, or somethin'.

Look in to Linux

[The Madpostal Worker]

The 2.4 kernels have really cool new routing abilities that do what you want, however it shure seems to be a while off.

You will have to clarify what you are doing

[anticypher]

How are you doing this, buying a service from your local provider, or creating your own cable network from scratch? If you are thinking of building your own, you will need to buy a headend router, which costs $$$$$$$.

What exactly are you hoping to achieve? Most cable modems have an ethernet connection to connect to your network. In home installations, the modem is really a router, with only a single IP address for a single computer.

Most cable modems are capable of offering up a range of IP addresses, certainly the newer DOCSIS modems have that capability. But it is up to the cable ISP to give/sell you a block of IP addresses instead of just a home user setup. Most cable operators in the US are only targeting the home market with 1 IP per connection, and have no idea how to offer their service to a business. Ask in advance, and don't rely on just calling their ordering line, go make an appointment with their sales department, and let them know you expect a professional level of service and are prepared to pay a slight premium for it. If you are trying to use someone like @HOME, they will cut you off if they detect a business use. They were promising to have a new service called @WORK real soon now, but I haven't seen it yet. @WORK is exactly the same as @HOME, except the T&C's allow you to use it for business use and maybe allow you to create a web server accessible from the internet, and of course it costs 4x the home service.

The way cable modems work, especially the new DOCSIS modems, is that there are several TV channels (6 MHz=~4.5 Mbps) devoted to the downstream connection (towards the user), and only one upstream TV channel (2-6 MHz=~1.2-4.5 Mbps). Typically the upstream channel is getting back to the headend through a series of carefully filtered reverse amps, usually on a channel which isn't propagated downstream by the regular repeaters. Don't count on being able to communicate from one cable modem in your building to another, or to use the cable as the replacement for a network. Their headend router may not allow one modem on the network to see any other modems on the network for security reasons (and also to prevent businesses like yours from doing exactly what you are proposing).

If you get just a single cable modem with a single IP address, then plug it into either a firewall running NAT, or a linux/BSD box with ipchains and ipmasquerading. Have 2 ethernet cards in the firewall/masqing machine, one to the cable modem, the other to your company network which will give all the machines access to the internet. Then you can rest a little easier about cybercriminals stomping all over your companies network (it'll keep the script kiddies out, anyways). Go read the various howto's on ipmasq, ipchains, cable modem connections, and anything else that looks reasonable. Go read cisco's web site, all their documentation is online and a lot of the technical stuff will give you a better understanding.

the AC

Multiple Cable Connections

[althiom]

Excuse me, but unless you have seperate providers the plan to have multiple cable connections would just be a waste of money. Unless I am mistaken, a cable provider provides a connection of say 170 kbs. Now if you have two cable connections you would have 170/2 kbs per connection or 85kbs. So where is the benefit? You could use VPN's and probably get the same results without the additional cost of the extra connections.

Have you considered xDSL ?

[Etyenne]

It might not be an option for you, but xDSL would probably better fit your need. Cable being a shared network, your multiple modem will all fight for the same bandwidth since they are all on the same (shared) cable network. xDSL is a point-to-point link, so at least the bandwidth to your ISP is constant (from there on, it's another story ...).

Re:Multiple Cable Connections

[wuzoe]

Around here, the actual cable "backbone" runs at around 40MB. Each user is throttled to less then 800kb or so. i.e. if I were to get more than one cable modem, they would each get their own 800kb.

(assuming the congested backbone isn't the limiting factor ... it depends on how popular they are in your area...)

But I gotta ask, considering the 800kb limit is only an artificial limit, can't you just ask the cable company for more bandwidth through the single modem?

dummynet

[marius]

FreeBSD has something called dummynet(4) that is integrated with ipfw(8) to allow QoS. It may be something to look into. You basically say that you want IP block X (can be a /32 block, or a host) to have Y /{B,kB,mB}/ of bandwidth. Very good stuff, I can limit my roommate's leeching of MP3's with it. I want some of the bandwidth I'm paying for too =]

Routers

[__aanonl8035]

As already mentioned, cable modems are typically setup on a shared network. The cable companies usually have 500+ houses/connections hooked up to one node. These connections all share the same bandwidth. Different cable modems have different capabilities, but to keep users from hogging up bandwidth the cable companies use various technologies to control the bandwidth to each user on the system (packet shaping) You may just want to ask if you get purchase a higher quality of service. Having said that... I use to work at an ISP with multiple T1s. Through the life of the ISP, there were multiple ways we load balanced. One way is to use the OSPF and select equal preference for the different interfaces out (the cable modems) and it will round robin packets through them. I suppose you could try to setup OSPF on a linux box using Zebra. [zebra.org] You could look into the packet shaping abilities of Linux. Search for packet shaper on freshmeat. Or you could buy a commercial product like the Packeteer. [packeteer.com]

Load balancing may be what you want.

[SwellJoe]

Sounds like what you need is load balancing. There are a couple of good options for this.

The most popular these days is Layer 4 switching, which splits traffic as evenly as it can by monitoring the traffic on each pipe and directing requests accordingly. Linux Virtual Server can provide L4 switching capabilities from any old box you've got lying around.

Cisco also produces intelligent routers that can perform a sort of load balancing. Another option is a cache heirarchy using Squid. Squid can perform basic load balancing functions through it's parent/sibling relationship features.

Probably the best thing to do is set up LVS as an L4 switch to load balance between Squids (one squid per pipe), with the Squid sharing cached content information via cache digests.

Using an L4 switch + cache setup you will not only effectively share the bandwidth you will also get faster response times and less bandwidth usage overall.

http://www.linuxvirtualserver.org [linuxvirtualserver.org]: Is the website to go to to find out about LVS. Also, the LVS kernel patches are now default in Red Hat 6.2 and above, plus Red Hat includes a web based administration frontend called Pirahna.

http://www.squid-cache.org [squid-cache.org]: The Squid homepage.

Hope this helps.

Thanks

[legana]

I'd almost given up hope of this question being posted. Thanks for your responses and I'll try some of them out. (At the moment we have each of the cable modems connected to dedicated pc's in various parts of the building, which works, but seems to be a waste when most of the modems are sitting idle a fair amount of the time.)